1. Field of the Invention
The present invention generally relates to electro-optical readers for reading indicia having parts of different light reflectivity, such as bar code symbols, during a multiple scan line mode and, more particularly, to an arrangement for, and a method of, producing an aiming spot with an enhanced visibility during a single scan line mode.
2. Description of the Related Art
Various electro-optical readers and scanning systems have been developed heretofore to read indicia such as bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths, and spaced apart from one another to bound spaces of various widths, said bars and spaces having different light-reflecting characteristics. The readers electro-optically decoded the coded pattern to a multiple alpha-numerical digital representation descriptive of the object. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. No. 4,251,798; U.S. Pat. No. 4,360,798; U.S. Pat. No. 4,369,361; U.S. Pat. No. 4,387,297; U.S. Pat. No. 4,409,470; U.S. Pat. No. 4,460,120 and U.S. Pat. No. 4,835,374, all of which have been assigned to the same assignee as the instant application.
As disclosed in some of the above patents, a particularly advantageous embodiment of such a scanning system resided, inter alia, in emitting a laser light beam from a hand-held, portable laser scanning head which was supported by a user; aiming the head and, more particularly, the laser light beam, at a symbol to be read; repetitively scanning the laser beam in a series of scan lines across the symbol; detecting the scanned laser light which is reflected off the symbol; and decoding the detected reflected light. Inasmuch as the laser light beam was usually, but not always, generated by a helium-neon gas laser which emitted red laser light at a wavelength of about 6328 Angstrom units, the red laser light was visible to the user and, thus, the user, without difficulty, could properly aim the head and position and maintain the emitted red laser light on and across the symbol during the scanning.
However, in the event that the laser light beam was generated by a semiconductor laser diode, as, by way of example, see U.S. Pat. No. 4,387,297; U.S. Pat. No. 4,409,470 and U.S. Pat. No. 4,460,120, then the aiming of the head relative to the symbol was rendered more difficult when the laser diode emitted laser light which was not readily visible to the user. For some laser diodes, the laser light was emitted at a wavelength of about 7800 Angstrom units, which was very close to infrared light and was on the borderline of being visible. Even with the advent of laser diodes whose emitted light was in the visible wavelength range, ambient light tended to mask out the laser diode light. Furthermore, if the laser diode light was moving, for example, by being swept across the symbol, and especially if the laser diode light was being swept at fast rates of speed on the order of a plurality of times per second, for example, at a rate of 40 scans per second, then the laser diode light was not readily visible to the user, even in a darkened room. Hence, due to one or more of such factors as the wavelength of the laser light, the intensity of the laser light, the intensity of the ambient light in the environment in which the laser light was operating, the scanning rate, as well as other factors, the laser diode light was rendered xe2x80x9cnon-readily visiblexe2x80x9d.
This non-readily visible laser diode light did not enable the user, however, to readily aim the laser diode light at the symbol, at least not without some difficulty and practiced effort because, simply put, the user could not see the laser diode light. The user, therefore, was required to hunt around by trial and error, hope that the scanning laser diode light was eventually properly positioned on and across the symbol, and wait until the scanning system advised him, typically by the lighting of an indicator lamp or by the sounding of an auditory beeper, that the symbol had indeed been successfully decoded and read. This hunting technique was a less-than-efficient and time-consuming procedure for reading symbols, particularly in those applications where a multitude of symbols had to be read every hour and every day.
In an attempt to enable the user to readily aim the laser diode light at the symbol, U.S. Pat. No. 4,835,374 proposed an aiming light arrangement to assist the user in visually locating and aiming the head at each symbol when non-readily-visible laser light was employed. The aiming light arrangement utilized a visible light source, e.g., one or more light emitting diodes, which was separate and distinct from the laser light source. A manually-operated trigger was employed to actuate the aiming light arrangement in a first operational state of the trigger for visibly illuminating a region on the symbol. This visible region was used for aiming purposes. Thereupon, in a second operation state of the trigger, the laser light source was actuated, thereby initiating the reading of the symbol.
Although the use of a discrete aiming light arrangement did assist the user in reliably aiming the head at the symbol, it was disadvantageous, primarily because it made the head bigger, heavier and less energy-efficient. The discrete light emitting diodes added some weight to the head, occupied space within the head, required separate electrical power and control circuitry, and consumed electrical power. It is desirable to make the head of such systems as lightweight, miniature, and efficient as possible.
Another advantageous embodiment of such a scanning system resided, among other things, in emitting the laser beam from a hands-free system which was not, or not always, supported by the user. The system was built into a stationary counter, or was configured as a workstation supported on a support surface for hands-free operation. In some installations, the head was removably supported in a stationary cradle for both hands-free and hand-held operation. Typically, the object bearing the symbol was brought to the hands-free system, rather than bringing the system to the symbol as was done with hand-held readers.
In any event, for both hand-held and hands-free operation, but especially for the latter, the laser beam was swept by a plurality of mirrors to create an omni-directional scan pattern having many intersecting scan lines. The symbol brought to the hands-free system would inevitably be read by one of the scan lines.
As advantageous as this multiple scan line pattern was in reading symbols, the visibility of each scan line suffered since the light intensity of the laser beam emitted by the laser diode had to be shared among all the scan lines. In a typical scenario, a rotating scan component having a plurality of mirrors, also known as a mirrored polygon, was rotated to reflect the laser beam to an array of additional reflectors for reflection to the symbol. The number of mirrors multiplied by the number of reflectors yielded a product signifying how many scan lines would be generated and, of source, the intensity of each scan line is the reciprocal of the product. The greater the number of scan lines, the dimmer each scan line, and the harder it is for the operator to see whether any scan line is registered with the symbol.
The problem of a dim scan line is particularly important when the operator wishes to read a symbol from a pick list. Many objects, due to their small size, cannot be printed with a symbol, or cannot be associated with packaging or a tag on which the symbol can be printed. For example, individual hardware such as screws, nails and like fasteners fit in this category. In order to process such objects, a printed catalog, known as a pick list, has a picture or description of each such object adjacent an appropriate identifying symbol. The operator at the check-out counter reads the symbol from the pick list by aiming one of the scan lines at the symbol. If the scan line is dim, then this aiming procedure is compromised.
Accordingly, it is a general object of this invention to avoid the above drawbacks of the prior art readers.
More particularly, it is an object of the present invention to eliminate discrete aiming light arrangements.
Still another object of the present invention is to enable a user to readily aim a laser beam emitted by a semiconductor laser diode on and across a symbol.
It is yet another object of the present invention to eliminate the trial-and-error hunting techniques, particularly at long working distances, in aiming a semiconductor laser diode beam at a symbol.
A still further object of the present invention is to increase the efficiency and reduce the time involved in optically reading a symbol with a semiconductor laser diode beam.
A concomitant object of the present invention is to accurately locate a symbol with a semiconductor laser diode-based scanner.
In keeping with the above objects and others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a reader for electro-optically reading indicia by reflecting a light beam off a plurality of generally planar light reflecting surfaces rotatable about an axis to sweep the light beam at a visibility across the indicia during a multiple scan line mode of operation. This invention proposes an arrangement for, and a method of, producing an aiming spot of enhanced visibility brighter than said visibility during a single scan line mode of operation.
In accordance with this invention, an actuatable light source is operative for producing the light beam; and an optical assembly is operative for directing the light beam along a path to the generally planar reflecting surfaces and to the indicia to be read. More particularly, a curved light reflecting surface is mounted for joint rotation with and between two of the generally planar reflecting surfaces. The curved reflecting surface is movable across the path. A controller is operative for actuating the light source during the single line mode to produce the light beam during movement of the curved reflecting surface across the path. The curved reflecting surface has a center of curvature on the axis for reflecting, and not sweeping across the indicia, the light beam incident on the curved reflecting surface at an angle of reflection which is substantially constant during movement of the curved reflecting surface across the path.
Hence, in accordance with this invention, an aiming spot of enhanced visibility is produced. During the single line mode, the light source is energized for only a small portion of each entire rotation of the reflecting surfaces. Preferably, the light source is energized shortly before the curved reflecting surface enters the path, and is deenergized shortly after the curved reflecting surface exits the path. A scan line is produced while the light source is energized. However, during the travel of the curved reflecting surface, the light beam is not swept and lingers on the symbol due to its constant center of curvature. The lingering beam forms a spot of greater visibility, and this spot is advantageously used for the aiming purposes described above.
In the preferred embodiment, all the reflecting surfaces are incorporated into a rotary scan component having the reflecting surfaces successively arranged in a circumferential direction about the axis. Additional curved light reflecting surfaces, each having the same center of curvature and each being mounted for joint rotation with and between adjacent pairs of the generally planar reflecting surfaces, may be incorporated into the scan component. Each curved reflecting surface is a circular arc.
Preferably, rotation of the scan component is maintained during both modes. The light source produces the light beam throughout the multiple line mode. However, the light source produces the light beam during the single line mode during movement of the curved reflecting surface across the path, but for only a fraction of each rotation of the scan component. Thus, the duty cycle of the light source during the single line mode is kept low.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.